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This paper presents a comprehensive simulation model of DC transit system with VSI-fed induction motor driven trains created using Power System Blockset (PSB) I MATLAB software package. The substation rectifier, the accurate track, the VSI-fed induction motor train and a detailed traction load are included in the model. The objective of this model is to study the short circuits faults that happen within the system. The model is used to simulate the train starting-up process, internal faults across DC-link capacitor and external faults across the third rail and the track. Analysis and conclusion of the simulation results are given, which shows the ineffectiveness 'of the conventional fault protection scheme in the DC transit system. Index Terms-Power electronics modeling, Power System Blockset (PSB)/MATLAB, 6-pulse three-phase bridge rectifier, sinusoidal pulse-width modulation (PWM), GTO voltage source inverter (VSI), DC transit system with VSI-fed induction motor driven train.

Linear ultrasonic motor has a wide range of applications in the aerospace field, which requires not only high accuracy of the control, but also the need for a stable running speed. For broadening its application, it is necessary to keep the linear ultrasonic motor having a stable speed. This paper first proposes AR module method for linear ultrasonic motor. The speed of the linear ultrasonic motor is measured by the driving and controlling system. By minimizing the targeted speed value and the actual speed value, we can keep the linear ultrasonic motor stable. This text also compares this method with the traditional PID method. The average deviation of AR is 24%.